1. Field of the Invention
The present invention relates to a shock absorbing front fork for bicycles. More specifically, the present invention relates to such a bicycle shock absorbing fork having struts with telescoping tubes with a shock absorbing system of a type which either does not include a hydraulic damping arrangement or has a hydraulic damping arrangement of a type in which the hydraulic damping fluid is contained within a separate cylinder or cartridge so as to be isolated from the walls of the telescoping tubes, so that the hydraulic damping fluid cannot be used as a source of lubricant for the telescopic tubes.
2. Description of Related Art
Numerous types of shock absorbing forks have been developed for absorbing the impacts experienced by the front wheel of the bicycle during off-road riding. Typically, these shock absorbing front forks have at least one strut formed of a pair of tubes which telescopically reciprocate with respect to each other under the influence of wheel shocks, and to absorb these shocks and damp the reciprocatory motion of the telescopic tubes, the strut contains a shock absorbing arrangement with or without a separate damping arrangement caused by uneven terrain encountered by the front wheel (see, e.g., U.S. Pat. Nos. 5,445,401 and 5,546,480).
In "high end" forks, hydraulic fluid damping is most commonly utilized in which a valve controls the flow of a hydraulic damping fluid between chambers on opposite sides of a damping piston. In most such hydraulic damping arrangements, the hydraulic fluid containing chambers are formed directly by inner surfaces of the telescopic tubes. Thus, since the damping fluid used is an oil or similar fluid which has the properties of a lubricant, the damping fluid, which is in direct contact tubes walls, is able to also serve to provide lubrication between the inner telescoping tube and the outer telescoping tube, in addition to serving as the damping medium. Examples of such, effectively self-lubricating, hydraulically damped shock absorbing front forks can be found in U.S. Pat. Nos. 4,971,344 and 5,088,705.
However, in many shock-absorbing suspensions for the front wheel of a bicycle, either no hydraulic damping is provided (see, for example, U.S. Pat. Nos. 5,284,352 and 5,470,090) or hydraulic damping is provided by a hydraulic fluid which is contained within a separate cylinder or cartridge. As a result, in the first type, there is no fluid to serve as a lubricant, and in the second case, the hydraulic damping fluid cannot be used as a source of lubricant for the telescopic tubes because it is isolated from the walls of the telescoping tubes. Since such telescoping shock absorbers still require lubrication against effects of the frictional forces between the telescoping members to be reduced, an external lubricant, such as grease, must be applied to the outside of the inner telescoping tube.
This external application of a grease has numerous detrimental effects. First of all, a coating of grease on the outside of the inner telescoping member is quite messy and open to exterior elements, which often results in the rider of the bicycle ending up with grease somewhere on their body if they accidentally brush against the front bicycle fork. Secondly, the grease wears off over time through extended use of the shock absorbers, and the grease needs to be reapplied to retain proper lubrication. Furthermore, since the grease is exposed to exterior elements, dirt and other contaminants stick to the grease and decrease its functional lubricating characteristics.
It is noted that telescopic motor vehicle compression springs are known (U.S. Pat. No. 2,683,034) where a reservoir of lubricating fluid is arranged to as to be dynamically loaded when an elastomeric compression spring is subjected to compression loading, thereby resulting in the lubricating fluid being forced out of the reservoir and distributed along the length of the elastomeric compression spring. Once the dynamic load is removed, excess oil is squeezed out of the lubricating channel, back to the reservoir. However, the arrangement of this patent is not applicable to the type of suspension described above in which hydraulic damping is provided by a hydraulic fluid which is contained within a separate cylinder or cartridge. Moreover, the presence of an incompressible fluid in the path of movement of the rigid body of such a cylinder or cartridge would produce a hydraulic locking of the telescoping tubes when the cylinder or cartridge dynamically engages the fluid.
Thus, a need exists for a way to avoid having to externally apply lubricants in shock absorbing front forks which are not of a self-lubricating type.